The present invention relates to cellular telephone systems and to modeling cellular telephone systems for optimizing utilization of the available overall radio spectrum. More particularly, the present invention relates to a reliable performance prediction based upon a measurement technique for unobtrusive gathering of data about the performance of the cellular system without interruption of normal operation and for complex analysis of the gathered data. The present invention relies upon wireless mobile unit location, geolocation, within a wireless communication system to provide location information and relies upon the measurement of the signal received from a number of mobile units by one or more sites in the system to provide path loss information. The present invention can alternatively rely upon the measurement of the strength of the signal received by the mobile unit. The present invention utilizes system information combined with geolocation and/or signal strength data to determine likely service areas, to establish network scoring, to analyize traffic patterns, blocked call and dropped call patterns and other network management functions.
The service area of a wireless communications system is partitioned into connected service domains known as cells, where radio telephone (cellular) users communicate, via radio links, with the base station serving the cell. The cells can be further partitioned into segments and individual antennae. Wireless systems are designed to provide the most effective coverage of a service area with the most efficient use of system resources, such as towers and antennae. In order to provide effective coverage, antennae tower locations must be carefully planned and antennae installations effectively utilized.
In order to allow mobile units to transmit and receive telephone communications as the units travel over a wide geographic area, each cell is normally physically positioned so that its area of coverage is adjacent to and overlaps the areas of coverage of a number of other cells. When a mobile unit moves from an area covered by one base station to an area covered by another base station, communications with the mobile unit are transferred (handed off) from one base station to another in an area where the coverage from the adjoining cells overlaps. Because of this overlapping coverage, the channels allotted to the individual cells are carefully selected so that adjoining cells do not transmit or receive on the same channels. Signals from all cell sites in an area of overlapping coverage will be received by a mobile wireless unit. Each cell site will also receive the signal from the mobile unit. However, because of the digital codes identifying each channel, the mobile wireless unit can identify the individual signals from individual cell sites. Further, because of the unique identifier associated with each mobile unit, the individual cell sites can identify the mobile unit associated with a given received signal.
When planning and establishing a wireless system, the geographic features of a location are considered as well as availability of antenna locations and likely areas of use. The systems planners use extensive design tools and techniques including practical algorithms for predicting path loss of signal transmission to determine an estimation of the potential coverage of the system once implemented. The system is then established with a set antenna pattern which can and will be adjusted and augmented as the system matures.
After the wireless system is operational, periodic testing is performed on the system to determine the extent and quality of coverage of the antennae in the system. The periodic testing and evaluation can be performed such as described and taught in co-pending application Ser. Nos. 09/567,709 and 09/09/236,572 incorporated herein by reference and in issued U.S. Pat. Nos. 5,926,762 and 5,970,394. Drive testing is a common method for the collection of path loss data within a wireless system. Drive testing collects actual measurements of the signal strength from specific towers received at specific locations throughout the wireless coverage area. One or more mobile receivers are transported throughout a representative portion of the cellular service area. Transportation is commonly accomplished by mounting the receivers in a vehicle and driving a predetermined path through the wireless system. The exact location of each receiver is monitored by means such as global positioning satellite receivers. The signal strength of wireless signals from specific towers in the system is determined by the receivers and correlated to the location of the receiver at the time of reception. The receivers can be tuned to particular frequencies or digital codes to identify the transmitting tower for a particular signal.
In order to develop an accurate representation of the effective coverage of a wireless system, the collected data must indicate both signal strength and location. Location of the collected data is determined by knowledge of the location of the mobile receiver at the time of the signal measurement. In order to optimize the coverage of a wireless system, it is necessary to know the strength of the coverage at a large number of different locations within the system. An accurate representation of the signal coverage can then be projected from interpolation of the path loss data, as fully described in co-pending application Ser. No. 09/567,709 fully incorporated herein by reference.
When data collection is obtained through drive testing a drive plan is established prior to the collection of data. The drive test is a carefully constructed route through a wireless system designed to optimize coverage collection and evaluation. In a first implementation of the present invention, unlike a drive test, data is collected from actual use of the wireless system and therefore the collection route cannot be planned. Data on signal strength is collected by measuring the signal strength of the wireless connection between actual subscribers and the cellular sites. Large amounts of data may be collected from some portions of the wireless system while sparse data may be collected from other portions. In an alternative implementation, data is collected from system use, however, the data is collected from a set of mobile units during a planned drive of the wireless system. In this embodiment, the spread of data is planned. The analysis of data collected through either implementation may be enhanced by the application of interpretation techniques applied to smooth the collected data and fill in gaps in the data.
Several methods for determining the location of a wireless unit within a cell system have been developed and deployed with varying accuracy and success. Wireless location systems can be handset-based in that the hand set acquires information about its position either relative to one or more cell sites or through independent positioning means such as a global positioning satellite system. The mobile unit makes an internal determination of its location and provides this information to the wireless system.
Wireless locations systems can also be network-based wherein the individual cells of the network obtain information about the location of the mobile unit relative to the individual cell sites and the network determines the location of the mobile unit by combining the information from the cell sites to triangulate the location of the mobile unit. For example, the difference in the time of arrival of the signal at each cell site or the difference in the phase angle of arrival at each cell site can be used to determine position.
Geolocation has found widespread application in the field of E-911 and E-411 services offered to cellular communication systems and subscribers. Examples of the application of geolocation of mobile wireless units can be found in the devices of True Position, Grayson Wireless Geometrix, SigmaOne, U.S. Wireless, CellLoc and others.